Electronic control device for intermittent operation of a windscreen wiper, particularly for motor vehicles

ABSTRACT

An adjustable electronic timing device for controlling the operating speed of windscreen wipers. A switch is provided for operating the wipers in either a continuous or an intermittent fashion. During intermittent operation, a programmable unijunction transistor (PUT) is caused to conduct to trigger an SCR which is connected in circuit to the wiper motor. A capacitor is charged during each wiping cycle and discharges at the termination of each wiping cycle to prevent retriggering of the SCR until the capacitor is fully discharged. The wiper operating frequency is adjusted by adjusting the resistivity of the discharge path for the capacitor. A braking circuit is provided for dynamic braking of the wiper motor.

United States Patent [191 Basso et a]. Jan. 1, 1974 [54] ELECTRONICCONTROL DEVICE FOR 3,364,410 H1968 Foreman 318/443 INTERMITTENTOPERATION OF A 3,335,352 8/1967 Neapolitakis 318/443 WINDSCREEN WIPER,PARTICULARLY FOR MOTOR VEHICLES Primary Examiner-B. Dobeck [75]Inventors: Eugenio Basso, Levico; Gaetano Atwmey 0strolenk et Viviani;Luigi Cartabia, both of Milano, all of Italy [57] ABSTRACT [73]Assignee: Fabbrlca Italiana Magnet: Mai-ell:

S.p.A., Milan, I y An adjustable electronic timing device forcontrolling [22] Filed: No 2, 1971 the operating speed of windscreenwipers. A switch is provided for operating the wipers in elther acontinu- 1 PP 194,968 ous or an intermittent fashion. Duringintermittent operation, a programmable unijunction transistor 30]Foreign Application Priority Data (PUT) is caused to conduct to triggeran SCR which s N 5 1970 I 1 connected 1n circuit to the wiper motor. Acapacitor IS 0V. ta y n charged during each cycle and discharges at thetermination of each wiping cycle to prevent retrig- [2?] 318/443, geringof the SCR until the capacitor is fully 3 2 charged. The wiper operatingfrequency is adjusted by 1 o earc adjusting the resistivity of thedischarge path for the capacitor. A braking circuit is provided fordynamic [56] References cued braking of the wiper motor.

UNITED STATES PATENTS 3,614,573 l0/l97l Rieman 318/443 6 Claims, 3Drawing Figures I PATENTEDJAN 1 I974 ELECTRONIC CONTROL DEVICE FORINTERMITTENT OPERATION OF A WINDSCREEN WIPER, PARTICULARLY FOR MOTORVEHICLES This invention relates to an electronic control device forcontinuously and/or intermittently operating windscreen wipers,particularly for motor-vehicles, of the design where at the beginning ofeach intermittent cycle the operating motor forthe wiping arms issupplied through a silicon controlled rectifier and then through thelimit switch, and where the beginning of each cycle is controlled by anelectronic timing circuit supplying the triggering signal to the siliconcontrolled rectifier.

The main object of the present invention is to provide a novel device ofthe above character, where the timing circuit can supply the triggeringsignal to the silicon controlled rectifier for the beginning of a newcycle only after the completion of the preceding cycle (limit switchmoving back to park or home position), so as to prevent the triggeringsignal frequency from exceeding the cycle frequency of the wiping arms.

Another object of the invention is to provide a timing circuit whichallows for the adjustment of the cycle frequency according torequirements and in which the beginning of the first cycle occursconcurrently with the connection of the intermitting circuit.

A still further object is to provide a very simple, economical andhighly reliable timing circuit.

According to the invention, the above objects are attained by a timingcircuit comprising a programmable unijunction transistor which iscontrolled by the voltage of a capacitor charging as the motor issupplied and discharging as the motor is braked, so as to cut off saidtransistor at the first step and to trigger it at the second step aftersome interval.

According to a preferred simple embodiment, the unijunction transistoris connected by its anode to the supply battery and by its cathode tothe control electrode of a silicon controlled rectifier, whereas itsgate is controlled by said capacitor which is charged by the motorsupply circuit through a unidirectional line and which is discharged ona circuit having a varying time constant. As the limit switch is alsoconnected to the motor supply circuit,'it is evident that only when saidswitch moves back to park or home position, the capacitor can discharge,reducing the gate voltage of the unijunction capacitor until it is belowthe anode potential, so that-a triggering signal is supplied to thesilicon controlled rectifier for controlling a new cycle.

Further features and advantages of the invention will become moreapparent from the description of the appended drawings, given by mereway of not limiting example, and in which:

FIG. 1 is the electric diagram of a windscreen wiper control circuitaccording to the invention;

FIG. 2 is a very approximate waveform diagram showing the shape of thevoltage vz. time across the operating motor for the wiping arms during afew cycles of the intermittent operation; and

FIG. 3 is also a very approximate waveform diagram showing the shape ofthe triggering voltage for the sili con controlled rectifier and thecharging and discharging voltage of the capacitor during a few cycles ofintermittent operation.

In the diagram of FIG. 1, by mere way of illustration, the controlportion of the circuit is shown at the right of line L, while the timingcircuit is shown at the left.

As well known, the control portion comprises the supply battery +B, thedouble-throw, three-point switch K,, the c.c. motor M and associatedlimit switch S, and the silicon controlled rectifier SCR. One of thethree points of switch K is the rest position R shown in FIG. 1, anotherpoint is the intermittent operation position land the third is thecontinuous operation position C.

The timing circuit according to the invention comprises the programmableunijunction transistor PUT having its anode A connected to battery +Bthrough the resistor R and the switch K, atposition 1, its cathode Kconnected to the control electrode of the silicon controlled rectifierand its gate G connected through resistor R to capacitor C at point F.Said anode A is also grounded through the parallel connection ofcapacitor C and resistor R the latter forming with R a supply voltagedivider for the anode.

In turn, said point F is both connected to ground through the fixedresistor R and the varying resistor R series connected with R and thesupply terminal H of motor M through the rectifier diode D and resistorR The limit switch S, shown at park or home position P, is alsoconnected with terminal H. Terminal H is also connected to groundthrough series connected of a capacitor C and resistor R,,.

In continuous operation, battery B will directly supply in known mannerthe motor M through the switch K at position C. At the end of operationand K at position R, as soon as limit switch moves back to position P,the motor is shorted and quickly stops.

In intermittent operation, the switch K is moved to position I, and thepositive pole of battery +B is applied through resistor R both to theanode of the silicon controlled rectifier SCR and to the anode A of theprogrammable unijunction transistor PUT.

Under these conditions, the silicon controlled rectifier SCR is notconductive because of not being triggered, while transistor PUT becomesconductive as the potential at its gate G is lower than that of anode A.Thus, the outlet current from cathode K provides for triggering thesilicon controlled rectifier SCR with resultant supply of motor M andactuation as well of the wiping arms which will start a first cycle(forward and backward stroke).

Just after starting, the limit switch S is moved to position Q, so thatthe supply for the motor is maintained through this switch and thesilicon controlled rectifier SCR is disconnected.

At the end of the cycle, switch K, being still at position I, switch Sis moved back to position P, the supply for the motor is cut off and theelectric braking for the motor is accomplished through the circuitcomrpising the resistor R FIG. 2 shows at T the supply time for themotor and at t,, 1 t etc., the instants at which braking begins. Time Tdepends on the vehicle windscreen glass cleaning degree and batteryvoltage, etc., and therefore can vary.

Moreover, during motor supply, capacitor C is charged through resistor Rand diode D and thus threr is also an increase of potential at gate G ofthe programmable unijunction transistore PUT connected through resistorR to capacitor C The potential at gate G is immediately raised to ahigher level than that at anode A, which assures that at this step notriggering signal can be supplied to the silicon controlled rectifierSCR from the cathode K, the programmable unijunction transistor PUTbeing cut off.

At the end of cycle (switch S at position P), the voltage across themotor will suddenly drop to zero (see descending port of curve in FIG.2) and the capacitor C disconnected from the terminal I-I due to theprovision of the rectifier diode D will discharge to ground through theseries resistors R and R Thus, the potential at the capacitor C, andgate G is reduced until the potential at gate G is lower than that atanode A, at which time the programmable unijunction transistor PUTtriggers, or is conductive again, the silicon controlled rectifier SCRis triggered again and the motor is started again to control a secondcycle.

FIG. 3 shows the shape of the potential at capacitor C,, and hence thepotential at gate G, at the charging and discharging steps of saidcapacitor, as well as the control pulses i i i acting on the siliconcontrolled rectifier SCR.

T is also the charging time for the capacitor C T, the discharging timeand V,, the potential at anode A of the PUT.

From the foregoing it will be apparent that a new triggering signalcould not appear on the silicon controlled rectifier SCR, and motorsupply and start as well, prior to total time T T, being elapsed, thatis until the end of the preceding cycle plus time T,

Since the discharge of capacitor C occurs through a circuit comprising avariable resistor R it is also apparent that by varying the insistanceof the latter, such as by means of a knob in the reach of the vehicledriver, this time T, can be reduced or increased from a minimumcorresponding to the connection of only resistor R. on the dischargecircuit to a maximum corresponding to the connection of R and R as awhole. As a result, this would correspond to the possibility of varyingthe time (T T,,) between the beginning of a cycle and that of anothercycle, or the cycle frequency.

The advantage of this control is evident, since depending on weatherconditions or vehicle glass dirt, the driver will accordingly adjust thecycle frequency. From the circuit it will also be seen that the firstcycle starts concurrently with the connection of the intermittentcircuit. Thus, as soon as switch K is moved to position I, capacitor Cis in a discharged state, whereby the potential of gate G is lower thanthat of anode A; thus, the programmable unijunction transistor PUT istriggered, followed by the silicon controlled rectifier SCR and thefirst cycle of the wiping arms is initiated concurrently. with theconnection of the intermittent circuit.

A further feature of the circuit is that the circuit is not affectedsudden variations in the battery voltage which could cause an untimelysupply of triggering signals to the silicon contr led rectifier SCR. Theprovision of capacitor C connecting the anode A to ground, assures acorrect operation of the circuit also under the conditions abovementioned.

According to an important aspect of the invention, the series circuit RCparallel connected with motor M and comprising the resistor R andcapacitor C is also effective as a protection against the untimelytriggerings of the silicon controlled rectifier SCR. This circuitprevents the SCR from being triggered again when the electric brakingfor the motor in initiated in the intermittent operation. Thus, at thistime the motor ceases to operate as such and acts as a generatorproviding a current switch (reversal) from inlet to outlet current.

The RC series circuit makes such current transients less abrupt, thusavoiding any re-triggering of the silicon controlled rectifier SCR.

Of course, the values for the resistor R and capacitor C are selected inconnection with the inductive characteristics of the motor, as thecircuit is one acting on the dispersed induction. It is obvious thatsuch a circuit RC can be applied to any windscreen wiper device having atiming circuit other than that shown.

A particular embodiment of the timing circuit has been described, but itis evident that the diagram shown can undergo changes, additions and thelike according to practical requirements without departing for this fromthe spirit of the invention. Thus, through slight variations, thecapacitor C, could act on the anode rather than on the gate of theprogrammable unijunction transistor PUT. In any case, the capacitor actsto to provide for triggering the programmable unijunction transistorPUT, or to cut off the same.

It is also apparent that the timing circuit can be applied to any otherc.c. motor having a braking circuit. Where the motor is of the permanentmagnet excitation type, resistor R is the braking resistance. On thecontrary, where the motor is a winding excitation motor, resistor Rwould correspond to the braking winding.

Finally, the braking circuit for the motor may be an electronic circuit,provided with or without a mechanical limit switch.

What is claimed is:

1. An electronic control device for a windscreen wiper motor having apair of input terminals comprising:

a supply source;

a wiper selector switch connected to said source;

a silicon controlled rectifier (SCR) for connecting said switch to afirst input terminal of said motor; said selector switch being operablebetween an open and a closed position; timing circuit means comprising aprogrammable unijunction transistor (PUT) having anode and cathodeelectrodes coupled between said selector switch and the triggerelectrode of the SCR and having a gate electrode; a timing capacitorcoupled between the remaining input terminal of the motor and said gateelectrode;

charging means coupled between said timing capacitor and said SCR forabruptly charging said capacitor when said SCR conducts;

said PUT being rendered conductive only when the voltage level at itsgate electrode is below the voltage at its anode to immediately triggerthe SCR into conduction upon closure of said selector switch;

said timing capacitor being adapted to charge to a voltage level higherthan the voltage level at its anode to prevent said motor from operatingfor a predetermined time interval after completion of one wiping cycle;

said motor means including switch means operated by said motor fordirectly coupling the first input terminal of said motor to said sourceas soon as the motor is energized to begin an operating cycle causingsaid SCR to be turned off and for disconnecting said motor from saidsource at the end of each wiping cycle;

3. The device of claim 1 further comprising a smoothing capacitorcoupled between the PUT anode and reference potential for smoothing theinput to the PUT anode. v

4. The device of claim 1 wherein said discharge means further comprisesan adjustable resistance element for altering the discharge rate of thetiming capacitor, said discharge circuit (R R of said control capacitor(C is of a variable time constant.

5. The device of claims 1 wherein said charging means comprises a diode.

6. The device of claim 1 further comprising series connected resistorelement and capacitor element coupled across the input terminals of themotor for preventing undesirable discharge of said timing capacitor andhence preventing spurious triggering of the SCR by the PUT.

1. An electronic control device for a windscreen wiper motor having apair of input terminals comprising: a supply source; a wiper selectorswitch connected to said source; a silicon controlled rectifier (SCR)for connecting said switch to a first input terminal of said motor; saidselector switch being operable between an open and a closed position;timing circuit means comprising a programmable unijunction transistor(PUT) having anode and cathode electrodes coupled between said selectorswitch and the trigger electrode of the SCR and having a gate electrode;a timing capacitor coupled between the remaining input terminal of themotor and said gate electrode; charging means coupled between saidtiming capacitor and said SCR for abruptly charging said capacitor whensaid SCR conducts; said PUT being rendered conductive only when thevoltage level at its gate electrode is below the voltage at its anode toimmediately trigger the SCR into conduction upon closure of saidselector switch; said timing capacitor being adapted to charge to avoltage level higher than the voltage level at its anode to prevent saidmotor from operating for a predetermined time interval after completionof one wiping cycle; said motor means including switch means operated bysaid motor for directly coupling the first input terminal of said motorto said source as soon as the motor is energized to begin an operatingcycle causing said SCR to be turned off and for disconnecting said motorfrom said source at the end of each wiping cycle; discharge meanscoupled across said capacitor for controlling the discharge rate of thetiming capacitor and thereby controlling the time interval between theend of a wiping cycle and the beginning of the next wiping cycle bycontrolling the time interval required for the voltage level applied bythe timing capacitor to the PUT gate electrode to fall below the voltagelevel at said PUT anode.
 2. The device of claim 1 further comprising avoltage divider coupled between said source and said PUT anode forcontrolling the voltage level applied to the PUT anode.
 3. The device ofclaim 1 further comprising a smoothing capacitor coupled between the PUTanode and reference potential for smoothing the input to the PUT anode.4. The device of claim 1 wherein said discharge means further comprisesan adjustable resistance element for altering the discharge rate of thetiming capacitor, said discharge circuit (R4, R5) of said controlcapacitor (C1) is of a variable time constant.
 5. The device of claims 1wherein said charging means comprises a diode.
 6. The device of claim 1further comprising series connected resistor element and capacitorelement coupled across the input terminals of the motor for preventingundesirable discharge of said timing capacitor and hence preventingspurious triggering of the SCR by the PUT.